In recent years, an increased number of electronic devices that require menu selections are equipped with touch panels, which allow users to touch the panel as guided by the screen display by a pen or a finger to select a desired menu. Such electronic devices use a wide variety of systems for identifying the location of a touch on the panel.
Patent Document 1 discloses a touch panel incorporating a liquid crystal display device that identifies the location of a touch by measuring the difference in voltage between a sensor line and a dummy line provided in the touch panel incorporating a liquid crystal display device. FIG. 21(A) is a plan view showing a part of the pattern arrangement in the display element section of a conventional touch panel incorporating a liquid crystal display device disclosed in Patent Document 1, and FIG. 21(B) is a cross-sectional view of the display element section, taken along the line Z-Z of FIG. 21(A).
The manner a touch panel incorporating a liquid crystal display device operates to identify a touch on the panel is briefly described with reference to FIG. 21. A touch panel incorporating a liquid crystal display device includes a TFT (Thin Film Transistor) substrate composed of a glass substrate 500 with a display element section 25 and driver circuits (not shown) formed thereon, and a CF (Color Filter) substrate composed of a glass substrate 800 with a color filter, a common electrode, and the like formed thereon. The substrates are disposed facing each other. On the glass substrate 500, not only a plurality of data lines 540, which are made of a conductive film, and a plurality of gate lines 510, which are made of a conductive film that is different from that of the data line 540, are arranged such that they cross each other, but also, for each of the data lines 540, a pair of a sensor line 550 and a dummy line 560 is formed in parallel with each other in the same layer as the data line 540, and for each of the gate lines 510, a pair of a sensor line 520 and a dummy line 530 are formed in parallel with each other in the same layer as the gate line 510.
In such touch panel incorporating a liquid crystal display device, when the surface of the CF substrate is pressed, a common electrode 840 formed on a surface of a sensor spacer 830 provided on the glass substrate 800 touches conductive pads 700 and 750 respectively connected to sensor lines 520 and 550, and the common voltage supplied to the common electrode 840 is supplied to the sensor lines 520 and 550 through the conductive pads 700 and 750, respectively. On the other hand, a reference voltage is supplied to dummy lines 530 and 560. The touch panel incorporating a liquid crystal display device compares the common voltage supplied to the sensor lines 520 and 550 against the reference voltage supplied to the dummy lines 530 and 560 to identify the location of the touch on the CF substrate.